Scroll apparatus for fluid compression or expansion are typically comprised of two upstanding interfitting involute spirodal wraps which are generated about respective axes. Each respective involute wrap is mounted upon an end plate and has a tip disposed in contact or near-contact with the end plate of the other respective scroll wrap. Each scroll wrap further has flank surfaces which adjoin in moving line contact, or near contact, the flank surfaces of the other respective scroll wrap to form a plurality of moving chambers. Depending upon the relative orbital motion of the scroll wraps, the chambers move from the radially exterior end of the scroll wraps to the radially interior ends of the scroll wraps for fluid compression, or from the radially interior end of the respective scroll wraps for fluid expansion. The scroll wraps, to accomplish the formation of the chambers, are put in relative orbital motion by a drive mechanism which constrains the scrolls to relative non-rotational motion. The general principles of scroll wrap generation and operation are discussed in numerous patents, such as U.S. Pat. No. 801,182.
Numerous attempts have been made to develop co-rotational scroll apparatus. Such apparatus provides for concurrent rotary motion of both scroll wraps on parallel, offset axis to generate the requisite orbital motion between the respective scroll wrap elements. However, most commercially successful scroll apparatus to date have been of the fixed scroll-orbiting scroll type due to various difficulties in achieving success with co-rotating scroll apparatus.
Typically, a number of rotary bearings are required in a co-rotational scroll apparatus, which decreases the reliability and efficiency of the machine. Furthermore, the typical co-rotating scroll apparatus have required a thrust bearing acting upon each of the scroll end plates to prevent axial scroll separation, thus substantially increasing the power requirements of the machine as well as substantially reducing the reliability of the machine.
An additional problem which must be dealt with in scroll apparatus, whether used for compression or decompression of fluid, are the forces which result from the fluid trapped in the chambers formed in the scroll wraps. These forces include an axial separation force component resulting from the fluid pressure upon the scroll element end plates and a radial separation force resulting from the fluid pressure upon the scroll wraps themselves. Furthermore, the separation forces due to the fluids compressed within the scroll elements vary cyclicly as the scroll elements rotate. This cyclic variation is a function of two factors. The first is the instantaneous location of each of the compression chambers formed by the scroll wraps during each revolution. The chamber location is a function of the angular and radial disposition of the center of the chamber with respect to the center of the scroll apparatus at a given crankangle. The second is the actual pressure of the compressed fluid, which varys according to the instantaneous location of the compression chamber in which the fluid is contained, decreasing from the radially inner ends of the respective scroll wraps to the radially outer ends thereof. Both these factors combine to produce a moment, the product of the instantaneous center of the compression chamber location and the instantaneous fluid pressure forces at that location. The resulting tipping moment upon the scroll member is the net effect of the moments developed by each compression chamber. The tipping moment acts perpendicularly to the axis of rotation of the scroll member, and therefore seeks to cause the tipping of the scroll element. Since the magnitude of the tipping moment is more pronounced at various crankangle positions during the rotation of the scroll element, actual tipping may occur at some crankangle positions, while it may be prevented at other positions by other forces sufficiently exerted on the scroll members. Actual tipping is observable as a rocking or nutation of the scroll member during rotation.
Typically, this is dealt with by the provision of an axial force acting to compress the end plates of the scroll elements together, in opposition to the separating fluid forces and by the provision of relatively larger bearings. These compressive axial forces are typically induced either mechanically by such means as thrust bearings or springs, or by fluid pressure imposed upon the opposite side of the scroll end plate.
Prior scroll apparatus attempt to counter the nutation effect by simply increasing the axial force loading upon the scroll end plate until the tipping moments are overcome, by providing a large number of bearings for supporting the scroll member shafts to prevent the shaft misalignment which occurs during tipping, and by decreasing the manufacturing tolerances of the components. All of these solutions increase the size and number of components of the scroll apparatus as well as the initial and operating costs, and also decrease the expected operating life of the scroll apparatus.
These solutions also undesirably affect the performance of the scroll apparatus as well. Because the axial force provided remains constant at any given operating condition, the axial force loading remains relatively high even when the separation effects of the tipping moment are low, which is typically the case during most of the scroll rotary cycle. Hence, there are unnecessarily high forces acting upon the scroll wrap tips at many crankangle positions in the scroll cycle, with resulting unnecessary friction and wear as well as excessive power consumption and loss of overall efficiency.
Furthermore, even when the axial force loading is relatively high, tipping of the scroll member can occur at some crankangle positions during rotation of the scroll apparatus. When nutation of the scroll element does occur, the scroll wrap tips can momentarily separate from the opposing scroll end plate. This permits fluid to pass from higher pressure compression chambers to lower pressure chambers, requiring recompression of the fluid and again reducing the overall efficiency of the scroll apparatus.
Therefore it is an object of the present invention to provide a scroll apparatus as will provide the highest possible efficiency while utilizing the least amount of power and therefore having the lowest power and least costly drive means.
It is a further object of the present invention to provide a method of reducing and compensating in a scroll apparatus at least in part for the net moment upon a rotating scroll member.
It is still a further object of the present invention to provide such a co-rotating scroll apparatus which is of simple construction and high operating reliability.
It is yet a further object of the present invention to provide a co-rotating scroll apparatus which is relatively compliant and not susceptible to damage in operation.
Finally, it is an object of the present invention to provide such a scroll apparatus as is suitable for and is relatively inexpensive in mass production.